This invention relates to sewage treatment and more particularly to method and apparatus for treatment of sewage on board ship employing the extended aeration principle.
Some examples of prior art devices for the treatment of sewage are disclosed in U.S. Pat. Nos:
U.S. Pat. No. 2,709,680--Watson (marine) PA1 U.S. Pat. No. 2,901,114--Smith et al. (concentric) PA1 U.S. Pat. No. 3,497,064--Valdespino (nested cone and cylinder) PA1 U.S. Pat. No. 3,552,725--Ray (rotor)
The Smith patent represents an effort to reduce treater size. The various chambers, however, are all of different diameters requiring a large inventory of parts. The air diffuser is said to create a rolling motion of the sewage in the aerator and to cause the contents of the stabilizer to rotate prior to discharge of the sludge therein back to the aerator. It does not appear that the motion imparted to the sewage in the Smith et al. treater is other than to increase air-solids contact.
The rotor of the Ray treater appears to be for the purpose of enhancing air circulation above a sewage pond.
The Valdespino treater includes an aerator disposed at a distance from a nested clarifier and chlorinator, with all three units having different diameters.
The Watson treater includes a power driven mechanical rotary agitator having blades to agitate the sewage. However, no aerator is included, merely subsequent stages of chemical treatment.
Other sewage treaters are discussed in the copending applications hereinafter mentioned and in the patents cited relative thereto.
Difficulties with prior treaters include cost, required variety of factory inventory, and size. An object of the present invention is to overcome these difficulties and still provide a highly efficient treater suitable for use on shipboard where the treater is subject to repeated changes of inclination.